1. Field of the Invention
The present invention relates to a transmission-power control assisting apparatus and a radio apparatus which notify information used for transmission-power control to be performed, based on an arriving wave reaching a local station, by a transmitting end of the arriving wave to the transmitting end in a radio transmission system, and to a radio terminal apparatus corresponding to the transmitting end.
2. Description of the Related Art
A CDMA (Code Division Multiple Access) system has been positively applied to a mobile communication system since it has confidentiality and interference immunity and a transmission-power control technology not only flexibly adaptable to multimedia and various modes of channel allocation but also capable of solving a near-far problem has been established.
FIG. 8 is a diagram showing a configuration example of a mobile communication system to which the CDMA system is applied.
In FIG. 8, an output of a RAKE receiving part 51 is connected to inputs of demodulating parts 52-F, 52-S and an Ec/Io measuring part 53-P. An output of the demodulating part 52-F is connected to an outgoing route of an upstream communication link and connected to one of inputs of an instruction selecting part 57 via a frame error measuring part 54-F, a frame error rate judging part 55-F, and a desired-value increase and decrease instructing part 56-F. An output of the demodulating part 52-S is connected to the outgoing route of the upstream communication link and connected to the other input of the instruction selecting part 57 via a frame error measuring part 54-S, a frame error rate judging part 55-S, and a desired-value increase and decrease instructing part 56-S. An output of the instruction selecting part 57 is connected to one of inputs of an Ec/Io judging part 59-P via a desired-value setting part 58, and an output of the above Ec/Io measuring part 53-P is connected to the other input of the Ec/Io judging part 59-P. An output of the Ec/Io judging part 59-P is connected to a corresponding input of an inserter 61 via a power-control-bit generating part 60, and an incoming route of a downstream communication link which makes a pair with the above upstream communication link is connected to a specific input of the inserter 61. An output of the inserter 61 is connected to a not-shown antenna system (used for forming a radio transmission path which is connected to a terminal 63), to which an input of the above RAKE receiving part 51 is also connected, via a spread processing part 62.
Incidentally, the RAKE receiving part 51, the demodulating parts 52-F, 52-S, the Ec/Io measuring part 53-P, the desired-value increase and decrease instructing parts 56-F, 56-S, the instruction selecting part 57, the desired-value setting part 58, the Ec/Io judging part 59-P, the power-control-bit generating part 60, the inserter 61, and the spread processing part 62 are provided in a radio base station of the above mobile communication system, and the frame error measuring parts 54-F, 54-S and the frame error rate judging parts 55-F, 55-S are provided in a base station controlling station which, in addition to performing channel control relating to a single or a plurality of radio base station(s) including the radio base station, operates in association with a switching network (mobile switch or the like) to perform call set-up.
In the mobile communication system as configured above, the RAKE receiving part 51 receives an arriving wave transmitted from the terminal 63 via the radio transmission path and extracts, from the arriving waves, components individually received via the following ‘pilot signal channel’, ‘primary channel’, and ‘auxiliary channel’ allotted to the terminal 63 under predetermined channel allocation and channel control.                the ‘primary channel’ which is allotted, when the terminal 63 originates, regardless of the kind of the call (for example, either a call to which a transmission service of an audio speech signal is provided or a call to which a transmission service of a data signal together with or not corresponding to the speech signal is provided) and which has a predetermined transmission capacity        the ‘auxiliary channel’ allotted together with the ‘primary channel’ to the call to which the data transmission service is provided        the ‘pilot signal channel’ whose transmission power is set to a ‘reference transmission power’ which serves as a reference of transmission powers of these ‘primary channel’ and ‘auxiliary channel’        
The Ec/Io measuring part 53-P finds a power proportion Ec/Io as a proportion of a level of thus extracted component of the ‘pilot signal channel’ to the sum total of levels of the above arriving waves.
Meanwhile, the demodulating parts 52-F, 52-S demodulate the components received via the ‘primary channel’ and the ‘auxiliary channel’, respectively, to generate base band signals for the respective components.
The frame error measuring parts 54-F, 54-S measure error rates of a frame sequence (hereinafter, referred to as a ‘frame error rate FER-F’ and a ‘frame error rate FER-S’) included in these baseband signals in a predetermined form.
The frame error rate judging pats 55-F, 55-S judge whether or not thus measured frame error rates FER-F, FER-S are lower than predetermined thresholds in parallel respectively.
The desired-value increase and decrease instructing parts 56-F, 56-S output binary information with a logical value of ‘1’ or ‘0’ indicating that a desired value for the above power proportion Ec/Io is to be updated to a larger value or a smaller value according to the ‘true’ or ‘false’ result of these judgments, respectively.
The instruction selecting part 57 outputs, depending on the logical value of the above binary information, binary information (hereinafter, referred to as an ‘increase and decrease instruction’) according to any one of the following rules.                one piece of the binary information outputted by the desired-value increase and decrease instructing part 56-F out of the desired-value increase and decrease instructing parts 56-F, 56-S        the other piece of the binary information outputted by the desired-value increase and decrease instructing part 56-S out of the desired-value increase and decrease instructing parts 56-F, 56-S        either one of the pieces of the binary information having a logical value of ‘1’ out of the binary information outputted by the desired-value increase and decrease instructing parts 56-F, 56-S        either one of the pieces of the binary information having a logical value of ‘0’ out of the binary information outputted by the desired-value increase and decrease instructing parts 56-F, 56-S        
The desired-value setting part 58 increments and decrements a previously set desired value for the power proportion Ec/Io (hereinafter, referred to as a ‘desired value’) by a predetermined value (>0) when the logical value of the increase and decrease instruction is ‘1’ and when, on the other hand, the logical value is ‘0’, respectively, thereby updating the desired value.
The Ec/Io judging part 59-P finds a difference between thus updated desired value and the power proportion Ec/Io found by the Ec/Io measuring part 53-P.
The power-control-bit generating part 60 generates a ‘power control bit’ whose logical value is set to ‘0’ when the difference exceeds a predetermined reference value, and set to ‘1’ when, on the other hand, the difference is lower than the reference value.
The inserter 61 inserts the above-mentioned ‘power control bit’ to a specific field, out of fields of individual frames given via the downstream communication link and including transmission information, which is secured in advance based on the forms of these frames.
The spread processing part 62 generates a transmission signal modulated according to the frame sequence to which the ‘power control bit’ is thus inserted and conforming to a predetermined CDMA system, and transmits the transmission signal to the terminal 63 via the above antenna system.
The terminal 63 extracts the above ‘power control bit’ from the frame sequence which is restored by the demodulation of the transmission signal.
The terminal 63 also increases or decreases the transmission power of the pilot signal channel depending on the logical value of the ‘power control bit’, and sets the transmission powers of the ‘primary channel’ and the ‘auxiliary channel’ to the products of two proportions which are given in advance or set (updated) based on the channel control procedure thereof by the transmission power, respectively.
In other words, the transmission powers of both the ‘primary channel’ and the ‘auxiliary channel’ are set in parallel at such values as to maintain the above-mentioned proportions relative to the transmission power of the ‘pilot signal channel’ which is increased or decreased as is described above in association with the radio base station.
Consequently, even when the combination of the radio channels allotted to the terminal 63 varies according to the mode of the communication service to be provided to the terminal 63, the transmission powers of these ‘primary channel’, ‘auxiliary channel’, and ‘pilot signal channel’ are maintained at such values as to maintain the above power proportion Ec/Io.
Incidentally, in the conventional art described above, for example, the ‘primary channel’ and the ‘pilot signal channel’ are allotted, and after the point in time when the ‘auxiliary channel’ is newly allotted to the terminal 63 to which the ‘auxiliary channel’ has not been allotted and the transmission via the ‘auxiliary channel’ is started (FIG. 9 (1)), the sum total of the powers of the arriving waves reaching the radio base station from the terminal 63 increases.
Therefore, the terminal 63 controls the transmission power of the ‘primary channel’ to be decreased so as to maintain the above power proportion Ec/Io after such a point in time (FIG. 9 (2)).
The transmission powers of these ‘primary channel’, ‘auxiliary channel’, and ‘pilot signal channel’ are increased step by step in parallel according to the logical value ‘1’ of the ‘power control bit’ continuously given from the radio base station (FIG. 9 (3)), thereby converging in proper values so as to solve the near-far problem (FIG. 9 (4)).
Further, since the time required for the transmission powers of these ‘primary channel’, ‘auxiliary channel’, and ‘pilot signal channel’ to converge in the proper values generally ranges from 10 odd seconds to 20 seconds (>20×10−3×100×4 decibel/0.5 decibel) due to the conditions described below, the deterioration in transmission quality mentioned above is difficult to be tolerated.                In order to obtain the above increase and decrease instruction with high precision, the above transmission quality has to be evaluated at least 100 times or more at a frame frequency of approximately 20 milliseconds.        In the case when the transmission via the ‘auxiliary channel’ is additionally started while the transmission via only the ‘primary channel’ and the ‘pilot signal channel’ is performed, the range in which the transmission power of the ‘pilot signal channel’ is to be varied generally becomes larger as the proportion of the transmission rate and the band of the ‘auxiliary channel’ to those of the ‘primary channel’ is higher, and is highly possible to become at least 4 decibels.        However, the increase and decrease amount of the above increase and decrease instruction is generally set to a small value of approximately 0.5 decibel.        
Further, in the above mobile communication system, a proportion of the sum total of bands of the ‘primary channel’ and the ‘auxiliary channel’ allowed to be allotted to a completed call that has occurred in the terminal 63 together with the ‘primary channel’ to the band of the ‘primary channel’ is highly possible to increase also in the future in accordance with the demand for provision of various modes of services such as ‘packet transmission’ and others.
Therefore, in such a mobile communication system, there has been a strong demand for a technology to solve the above deterioration in the transmission quality with high reliability without impairing the solution of the near-far problem based on the predetermined transmission-power control.